The present invention relates to a process for the oligomerization of hydrocarbon feedstocks using commercial hydrotreating catalysts in the absence of hydrogen. In particular, the present invention relates to a non-hydrogen consuming process for the oligomerization of hydrocarbon feedstocks using hydrotreating catalysts which remain active in the presence of sulfur.
Recent work in the field of olefin upgrading has resulted in a catalytic process for converting lower olefins to heavier hydrocarbons. Particular interest is shown in a technique developed by Garwood, et al., as disclosed in European Patent Application No. 83301391.5, published 29 Sep. 1983, incorporated herein by reference. Distillate range hydrocarbons can be synthesized over ZSM-5 type catalysts at elevated temperature and pressure to provide a product having substantially linear molecular conformations due to the ellipsoidal shape selectivity of certain medium pore catalysts.
Conversion of olefins to gasoline and/or distillate products is disclosed in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens, Plank and Rosinski) wherein gaseous olefins in the range of ethylene to pentene, either alone or in admixture with paraffins are converted into an olefinic gasoline blending stock by contacting the olefins with a catalyst bed made up of a ZSM-5 type zeolite. In U.S. Pat. No. 4,227,992, Garwood and Lee disclose the operating conditions for the Mobil Olefin to Gasoline/Distillate (MOGD) process for selective conversion of C3+ olefins to mainly aliphatic hydrocarbons. U.S. Pat. Nos. 4,150,062 and 4,211,640 (Garwood et al.) disclose a process for converting olefins to gasoline components. In a related manner, dimerization of propene with impregnated ZrO2/SO4 or ZrO2/WO3 catalysts is described in U.S. Pat. No. 5,113,034.
In the process for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using a medium pore shape selective acid crystalline zeolite, such as ZSM-5 type catalyst, process conditions can be varied to favor the formation of hydrocarbons of varying molecular weight. At moderate temperature and relatively high pressure, the conversion conditions favor C10+ aliphatic product. Lower olefinic feedstocks containing C2-C8 alkenes may be converted; however, the distillate mode conditions do not convert a major fraction of ethylene. A typical reactive feedstock consists essentially of C3-C6 mono-olefins, with varying amounts of nonreactive paraffins and the like being acceptable components.
The improvement of the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids has been the subject of extensive research and development in the petroleum industry for many years. This research has led to the introduction of a number of superior polyalpha-olefin (PAO) synthetic lubricants produced by the oligomerization of alpha-olefins or 1-alkenes. In terms of lubricant property improvement, the industrial research effort for synthetic lubricants has been toward fluids exhibiting useful viscosities over a wider range of temperature, i.e., improved viscosity index (VI), while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. These new synthetic lubricants exhibit lower friction characteristics and are, therefore, capable of increasing mechanical efficiency of various types of equipment including engines, transmissions, worm gears and traction drives, over a broader range of operating conditions than mineral oil lubricants.
PAO lubricants are often formulated with additives to enhance those properties for specific applications. Among the more commonly used additives are oxidation inhibitors, rust inhibitors, metal passivators, antiwear agents, extreme pressure additives, pour point depressants, detergent-dispersants, viscosity index (VI) improvers, foam inhibitors and the like. This aspect of lubricant technology is described in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., 14, 477-526, to which reference is made for a description of the use of such additives.
PAOs useful as synthetic base stocks or functional fluids may be synthesized by homogeneous catalysts, such as promoted BF3 or AlCl3 catalysts. The synthesis of PAOs with a promoted BF catalyst is discussed in the Theriot et al. U.S. Pat. No. 5,171,905. The PAO processes using homogeneous catalysts always include a complicated and tedious catalyst separation step. For example, the promoted BF3 or AlCl3 catalyst is usually deactivated and destroyed by washing with sodium hydroxide, dilute acid and water consecutively.
One of the problems with commercial catalytic oligomerization processes presently being used is the rapid deactivation of the catalysts in the presence of even low levels of nitrogen and sulfur in the feed stream. Therefore, there is a need for a catalytic hydrotreating process which can oligomerize chemicals in nitrogen and sulfur contaminated feed streams without a substantial reduction in the reactivity of the catalyst.